Influence of organic molecules on wetting characteristics of mica/H2/brine systems: Implications for hydrogen structural trapping capacities

Hypothesis: Actualization of the hydrogen (H-2) economy and decarbonization goals can be achieved with feasible large-scale H-2 geo-storage. Geological formations are heterogeneous, and their wetting characteristics play a crucial role in the presence of H-2, which controls the pore-scale distribution of the fluids and sealing capacities of caprocks. Organic acids are readily available in geo-storage formations in minute quantities, but they highly tend to increase the hydrophobicity of storage formations. However, there is a paucity of data on the effects of organic acid concentrations and types on the H-2-wettability of caprock-representative minerals and their attendant structural trapping capacities. Experiment: Geological formations contain organic acids in minute concentrations, with the alkyl chain length ranging from C-4 to C-26. To fully understand the wetting characteristics of H-2 in a natural geological picture, we aged mica mineral surfaces as a representative of the caprock in varying concentrations of organic molecules (with varying numbers of carbon atoms, lignoceric acid C-24, lauric acid C-12, and hexanoic acid C-6 ) for 7 days. To comprehend the wettability of the mica/H-2/brine system, we employed a contact-angle procedure similar to that in natural geo-storage environments (25, 15, and 0.1 MPa and 323 K). Findings: At the highest investigated pressure (25 MPa) and the highest concentration of lignoceric acid (10(-2) mol/L), the mica surface became completely H-2 wet with advancing (theta(a) = 106.2 degrees) and receding (theta(r) =97.3 degrees) contact angles. The order of increasing theta(a) and theta(r) with increasing organic acid contaminations is as follows: lignoceric acid > lauric acid > hexanoic acid. The results suggest that H-2 gas leakage through the caprock is possible in the presence of organic acids at higher physiothermal conditions. The influence of organic contamination inherent at realistic geostorage conditions should be considered to avoid the overprediction of structural trapping capacities and H-2 containment security. (C) 2021 The Authors. Published by Elsevier Inc.